1. Field of the Invention
The present invention relates to a scroll type compressor suitable for use as a refrigerant compressor for an automobile air-conditioner.
2. Description of the Related Art
Such a scroll type compressor is disclosed in numerous patents and references and the principles behind its operation are well known.
In a scroll type compressor, several hermetic spaces are created enclosed by a plurality of contact lines formed by a fixed scroll member and movable scroll member engaging with each other. When the movable scroll member performs revolutionary motion, the contact lines move from the outer periphery toward the center along the walls of the spiral bodies. Along with this, the enclosed hermetic spaces also move toward the center and compresses a refrigerant or other fluid while being reduced in volume.
Since a plurality of these contact lines are formed, however, the shapes of the spiral bodies must be kept to an error from the predetermined shapes on the order of several microns. Further, strict precision of the relative positions of the two scroll members is required. If these errors become too great, they end up separating at one of the plurality of contact lines and the hermetic degree of the space to be hermetically sealed falls, so the amount of discharge falls, the power consumption rises, and an abnormally high temperature operation state is caused. Accordingly, in a scroll type compressor, it is necessary to make the precision of processing of the spiral bodies and the precision of assembly of the two scroll members extremely high. This is the main reason why scroll type compressors were not put into practical use for a long time. There are also various difficulties even with today's processing technologies and assembly technologies.
To solve these problems in a scroll type compressor, proposal has been made in numerous patent specifications of a means for changing the radius of the revolutionary motion of the movable scroll member along with the shape of the scroll member. For example, in the compressor disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2-176179, the end of the shaft is provided with a drive projection having a planar face, the bush for giving revolutionary motion to the movable scroll member is provided with a groove having a planar face, and the drive projection is fitted slidingly in the groove. It has been proposed that the planar face of the drive projection be inclined with respect to the line connecting the center of the bush and the center of the shaft in the direction opposite to the direction of rotation of the shaft.
If this construction is adopted, the bush receives a compression reaction force from the movable scroll member engaged in the revolutionary motion. Due to this reaction force, the bush moves along the planar face of the drive projection. As a result of this movement and due to this positional relationship, the distance between the center of the bush and the center of the shaft, that is, the radius of revolutionary motion, becomes larger than the state before movement. This is due to the fact that while the movable scroll member is revolving, a force acts so that the radius of revolution always becomes larger and that even if there is some error in the formation of the scroll members, the movable scroll member adjusts its radius of revolution along with that shape and reliably forms the contact lines.
With the above configuration, however, several problems occurred at the time of liquid compression. That is, the refrigerant would liquefy and flow into the compressor if it were stopped for a long period of time. If the compressor were started from this state, the refrigerant would be compressed as a liquid in the compressor, an abnormally high pressure would be caused, and the abnormally high pressure would cause breakage and seizure of the scroll teeth, damage to the discharge valve, and burnout at the frictional face of the solenoid clutch, not shown. Therefore, by operating the compressor so that the movable scroll member moves with respect to the fixed scroll member while the compressor is idle, that is, in a state where the radius of revolution becomes smaller and a clearance is caused between side faces of the scroll members in the time after startup until the compression reaction force becomes sufficiently large, it is possible to mitigate the sharp rise of the load on the vehicle engine and to prevent in advance vibration and shock at the time of startup of the compressor.
In practice, however, it is difficult to arrange enough of a balance weight to completely balance the centrifugal force of the movable scroll member due to the size involved, so due to the remaining centrifugal force of the movable scroll member, the movable scroll member ends up moving in the direction giving a larger radius of revolution immediately after startup. As a result, full use is not made in practice of the function of mitigation of the startup load.
Even at startup accompanied with liquid compression, for the same reason as with the residual centrifugal force, the radius of revolution increases immediately after startup, the clearance between side walls of the scroll members decreases, a rise in liquid pressure is immediately caused, and as a result various problems arise such as slipperiness of the frictional face of the solenoid clutch causing burnout, generation of abnormal noise due to sudden liquid compression, and damage to the scroll members. However, these are problems which can be prevented in advance by making sufficient use of the mitigating function on the startup load in the same way as above.